The invention relates to a circuit arrangement comprising at least two amplifiers with different electrical properties, one of which is in operation at a time, the amplifier being multi-stage amplifiers having feed-back paths or branches which serve to stablize the DC voltage. The feed-back branches are separated with respect to the DC current by isolation capacitor means and are connected via further capacitor means to a reference potential.
In radio receivers, for example, different amplifiers are required for processing a signal depending on whether there is AM or FM operation. Very different amplifier circuits are required in intermediate frequency amplifiers because of the different types of modulation--amplitude modulation or frequency modulation.
In the case of integrated circuits a common amplifier is frequently used for both types of operation; however, parts of the amplifier circuit are replaced by other parts depending on the type of operation and it is possible that the operating point is switched. This circuit construction has the disadvantage that it is not possible to provide optimum dimensioning because of the dual function of the amplifier. The TDA 1083 circuit produced by AEG-TELEFUNKEN for example contains a common switchable intermediate frequency amplifier for optional AM or FM operation.
It is possible to provide optimum dimensioning of the amplifier circuit if a separate intermediate frequency amplifier is provided for AM and FM operation. This circuit construction has the disadvantage that more connections (pins) are required and the number of components in this circuit as well as the number of components connected externally is greater.